In epithelial tissues, cells communicate with their neighbors and receive information from the surrounding environment through signaling networks, secreted and adhesion molecules, and junctional proteins in order to form complex organs, and to maintain their integrity and morphology. This robust self-organizing system, however, is progressively disrupted during malignant overgrowth. In the proposed studies, we will address how certain mutant cells can deviate from the robustly organized epithelial microenvironment to undergo uncontrolled overgrowth using the Drosophila wing imaginal disc model system. Within this system, specifically, we looked at the epithelial folds of the wing hinge region. In this tissue microenvironment, conserved neoplastic tumor-suppressor gene (nTSG) mutant cells delaminate from the apical side of the epithelium and start uncontrolled overgrowth by exploiting endogenous JAK/STAT inflammatory signaling activity. In contrast, these mutant cells in the wing pouch area are normally extruded from the basal side of the epithelial layer and undergo apoptosis. We show that the hinge area display a network of specific and robust basal structures, including a web of intertwining filopodia and enriched basal microtubule cytoskeleton. We hypothesize that the cytoarchitectural structures in the hinge area force nTSG mutant cells to delaminate from the apical side and enter the lumen, where JAK/STAT activity is high, allowing uncontrolled cell growth in a ?niche-like? microenvironment. We plan to test the hypothesis and, thereby, to accomplish the objectives of the application by pursuing the following three specific aims: (1) To determine how the direction of nTSG-LOF-cell delamination is regulated and its relationship to dysregulated cell proliferation; (2) To determine how local JAK- STAT signaling is involved in regulating uncontrolled cell growth; and (3) To determine the role of cell competition in different tissue microenvironment. The expected outcomes from these aims will advance understanding of mechanisms underlying the initial stages of malignant growth. Given the conservation of the epithelial cell organization, understanding these regulatory mechanisms will therefore provide new insights into how tissue-intrinsic microenvironment determines whether malignant growth can actually be induced after cells acquiring tumorigenic mutations. The proposed studies will ultimately propel the development of new therapeutic avenues for preventing or managing cancer at an early stage.